Berry Berry Easy will continue on with the notes about “Liquid and Solid State” with Part 2 in the series. In Part 1, we touched on the changes of state of matter, kinetics theory of liquid and the structure of liquid. This part will be all about crystal lattice. It is another easy portion of the topic as with the previous part. But whenever possible, do try to visualise the crystal lattices and learn to differentiate the characteristics graphically. It is the easiest way to understand this topic. It will also be useful to know more examples of each type of crystal systems than the one being quoted in the notes below. So pick up your pencil and some paper, and let the sketching of crystal lattices begins. (Do refer to books or references online too while you sketch).
STPM Chemistry Form 6 – Terminology and Concepts: Liquid and Solid States (Part 2)
Crystal lattice – regular arrangement of atoms, molecules or ions in a crystalline solid.
Unit cell – a small repeating unit that contains a group of particles (atoms, ions or molecules) in a crystal.
There are 7 crystal systems (primitive unit cells – all the lattice points are placed at the corners of the cell only):
|Cubic||a = b = c<a = <b = <c = 90˚||Sodium chloride|
|Tetragonal||a = b not = c<a = <b = <c = 90˚||Tin|
|Orthorhombic||a not = b not = c<a = <b = <c = 90˚||Rhombic sulphur|
|Monoclinic||a not = b not = c<a = <b = 90˚<c not = 90˚||Monoclinic sulphur|
|Triclinic||a not = b not = c<a not = <b not = <c not = 90˚||Copper(II) sulphate, potassium dichromate(VI)|
|Rhombohedral||a = b = c<a = <b = <c not = 90˚||Calcite (calcium carbonate)|
|Hexagonal||a = b not = c<a = <b = 90˚<c = 120˚||Quartz, graphite|
There are 7 multi-primitive lattices (lattice points are located not only at the corners, but also at the faces or centres of the cells).
There are 14 types of crystal lattices.